Midget Maintenance - Open Wheel

Open-wheel cars have gained their name because they simply don’t have fenders. This leaves many of the crucial components exposed while racing subject to contact with other race cars, inside barriers, and the outside walls. So this being said, it’s necessary to thoroughly inspect the chassis’ suspension system and driveline. Most importantly, this helps to insure many safety aspects before putting the car back on the racetrack.

In this article we will go over post/pre race inspection and regular maintenance of an open wheel Midget race car, also known as Speed Cars. In some cases, these types of race cars nearly get completely disassembled after every race. This sounds like a lot of work, but Midget race cars are surprisingly easy to work on. You can change a rear axle with the differential in less than a half hour if need be, and there are some nights at the track you have to!

The first matter to be handled is washing the clay off the car—no one likes working on a dirty race car. Once this has been achieved, the next task is to disassemble the suspension components and check if the car is still in “square.” The suspension in the rear of these cars is a torsion bar type arrangement, and the front of the car is a coilover shock absorber type. All four shock absorbers, torsion bars, and coil springs need to be pulled off the car. The torsion bar and the bushings the bars ride on need to be cleaned and re-greased. It’s a good idea to simply plunge the shock up and down a few times and visibly check to see if the shaft is bent or hung up. Some open wheel racers run their shocks on a shock dyno after every race to make sure the compression and rebound is within specification. We would recommend doing this at least once a season or if the car is not properly responding to suspension adjustments.

Squaring and Leveling the Rear Axle

Set the rearend in the chassis with the torque tube, driveline, and ball housing fully assembled. Prop the axle up on squaring blocks between the bottom framerail and bottom of axle. The driveline must be parallel to the lower framerail and torsion arms. The squaring block height is crucial. Install the birdcages on the axle with the wheel spacers and axle nuts to hold the birdcages in place. With the radius rods and torsion arms disconnected measure from the center of the axle to the front of the motor plate. This measurement can vary depending the brand of chassis. The car pictured has a 33.5-inch wheelbase. So we need to adjust the axle until we achieve the same measurement on the right and left side of the car. Once the axle is square, connect the radius rod to the top of the birdcage with the radius rod free to lengthen or shorten. Now with a digital smart level time the birdcages. There is a flat on the back side of the birdcage where you position the level to 90 degrees, or a degree or two forward depending set up preference. Use the radius rods to dial in timing by screwing it in or out. Next tighten the pinch clamps on torsion arms to the torsion bars. With the torsion stops loose bring the torsion arm up to birdcage and put it through the slider bolt. Make sure the slider bolt is cleaned, freshly greased, and is not binding up. Next, hook up the Jacobs ladder to the clevis on the top of the birdcage. Make sure the pin slides through the clevis easy and is not bound up. Adjust heim joint until the ladder is free.

4/21<strong>2 </strong>With the shocks off the car, compress them and inspect for any binding, bent shafts, or leaks before reinstalling them.

Front Axle Alignment

Next we take a look at the front axle alignment. Place setup blocks between the lower framerail and the front axle. The height of the block will also determine the ride height of the car. Typically, the setup blocks are around 3 inches depending on the chassis make. Like the rear axle, we take a measurement from the center of the axle to the front of the motor plate. On this car the measurement is 38.5 inches. Most racers run the axle square so the measurement is the same on the right and left side of the car. Some open wheelers will run the right side of the axle a fraction of an inch further out then the right to help the car turn. Once the axle is square, we set the caster. Place the digital level on the right front king pin. We want approximately 12 degrees of negative caster. Dial this in by turning the radius rods that are connected to the front axle. Negative caster helps transfer weight to the rear wheels. The next step is to set the Panhard bar. Start by sliding the Panhard bar to where it’s level with the front axle then move it to your starting point from there. Most racers will move it up 1/8- to 1/2-inch to start the night. Moving the Panhard down pushes the front axle over to the right, which puts more weight on the front right tire. Next we need to set the toe of the front tires. Most racers run about a 1/4-inch of toe out. This enables the car to drive straight down the straightaway. The toe is set by measuring the distance from the front of the right rim to the front of the left rim then using the same method measure the back of the rim. The difference is the toe and it can be adjusted using the radius rod that runs from the right spindle to the left spindle.

The ride height on the front is already set with the 3-inch setup block, so install the shock absorbers and coil spring. Wind up the spanner nut until it’s tight up against the coil spring.

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Now it’s time to set the ride height. Remove the squaring blocks from the rear axle and replace them with the set-up blocks. The setup block height is typically three and a half inches, but can vary depending on the racers preference. Now install the torsion stops on the torsion bars, making sure the adjuster bolt is backed out. Leave an 1/8-inch of clearance between the adjuster bolt and the torsion stop adjuster pad. Tighten the torsion stop to the bar and screw the adjuster nut in until it hits the stopping pad. Then give the adjuster bolt a 1/8-inch of pre-load on the bar. Remove blocks and rear height is set.

18/21<strong>15 </strong>Now remove the squaring block from the rear axle and install the setup blocks. The setup block height is typically 31/2 inches, but can vary depending on the racers preference. Install the torsion stops on the torsion bars, making sure the adjuster bolt is backed out. Leave an 1/8-inch of clearance between the adjuster bolt and the torsion stop adjuster pad. Tighten the torsion stop to the bar and screw the adjuster nut in until it hits the stopping pad. Then give the adjuster bolt a 1/8-inch of pre-load on the bar. Remove blocks and rear height is set.

Next, check the driveline. Pull the bellhousing off and inspect the torque ball. Make sure there is no gulling on the riding services. Also make sure the universal joint does not have excessive play in it. If this all checks out well then re-grease the U-joint and bellhousing. Also, when the car is off the stands and on the ground, make sure the torque tube turns freely and is not bound up. It’s a good idea to have someone stand on the back bumper and check to make sure the torque tube is free when weight is applied. The driveline is directly under the driver’s feet so this not only affects the handling of the car, but can be a safety issue as well.

19/21<strong>16 </strong>With the right height set, set the torsion stops.

20/21<strong>17 </strong>After inspecting the torque ball, make sure there is no gulling on the riding services. Make sure the U-joint doesn’t have excessive play, then re-grease the U-joint and bellhousing. When the car is off the stands and is setting on the ground, make sure the torque tube turns free and is not bound up.

Scaling

21/21<strong>18 </strong>Lastly, scale the car to ensure the corner weights are where they should be.

The last thing to do before heading to the racetrack is to scale the car. This helps to ensure all your previous work is correct. Not all teams use this method, but it certainly does not hurt to do so. The scale weights will tell you how much weight is dispersed per tire. It will also tell you cross weight, rear weight, and overall weight.